Liver hepatocytes will be used to investigate the turnover of Ado-met. The same system will be used to monitor the rate of methionine catabolism under a variety of cellular methionine concentrations. Additionally attempts will be made to determine tissue concentration of 3-methylthiopropionate and to determine its rate of turnover. The rate of turnover of methionine, Ado-met and 3-methylthiopropionate will be compared in order to estimate the relative importance of the transaminative and transsulfuration pathways of methionine catabolism under a variety of methionine loads. Because we have shown that the decarboxylation of methionine can be carried out by the liver mitochondria, as well as the cytosol, additional work will be carried out to investigate the role of these two decarboxylation systems in methionine catabolism. The extent and nature of the competition between the keto acid of methionine and the keto acids of the branched chain amino acids and phenylalanine and tyrosine will be investigated.